This invention relates to a process of wrapping a strip-like flexible repair substrate around a cylindrical structure. An edge of the repair substrate aligns with a visible indicia along the length of the previously wrapped repair substrate to control the amount of overlap, or helix pitch, between adjacently wrapped substrate layers. The indicia allows a consistent overlap, the amount of overlap desired being dependent upon the application and amount of strength required for the repair.
Pipe systems provide basic utilities to the public, such as water, gas, petroleum, and sewage. These basic utilities and petroleum pipeline operators are often heavily relied upon by the public. As such, the pipe systems are usually in a state of full operation, i.e. optimal flow rate. There is usually a very limited amount of time that the pipes and pipe systems operate at a reduced flow rate, while not seriously affecting utility service.
Pipelines and other cylindrical structures, whether above ground or below, occasionally suffer damage. Over time, these cylindrical structures can be damaged from rust, corrosion or other degradation. Further, the damage can occur during repair or installation, for example from tool impact or falling debris.
At a damaged area of the pipe, there is a smaller cross-sectional thickness of the pipe. The thickness of the pipe is inversely proportional to the hoop stress of the pipe, i.e. the circumferential stress in the pipe due to the operational fluid pressures in the pipe. Accordingly, there is a larger hoop stress in the damaged area as compared to the rest of the pipe.
The hoop stress in the pipe is proportional to the strain in the pipe. Therefore, the larger hoop stress in the damaged area results in a proportionally larger strain. The larger strain in the damaged area of the pipe causes further damage. Consequently, the flow through the pipe, and resulting pressure therefrom, is usually reduced or stopped to prevent further breakage or leaking from the structure until the pipe is repaired or replaced. This flow reduction is undesirable because the utility service is correspondingly reduced.
It is usually more cost effective to permanently repair the leaking pipe rather than replace it. When the damaged pipe is replaced, the downtime of the system, the labor costs, the material costs, as well as the costs associated with the loss of utility services are usually large.
An expedient method of repair involves, at least in part, applying a structural reinforcement by way of wrapping the structure with a flexible repair substrate. Such flexible substrates are commonly tapes (defined principally by films) woven fabrics, and non-woven fabrics. Non-woven fabrics are characterized by the non-parallel, random organization of the component fibers, for example, paper. The flexible substrates are often used in conjunction with various adhesives, resins, putties, and fill materials.
The flexible repair substrate has a characteristic tensile strength of its own. The substrate preferably is tensioned or pulled when surrounding the pipe undergoing fluid pressures. In the finished repair, the several turns of the substrate about the pipe are in tension, thus applying to the pipe a compressive force pattern which acts in the pipe counter to hoop stresses created by pressure of the fluid in the pipe. When the pipe is strained by internal fluid pressure, the repair substrate in the repair also strains proportionally to share hoop stress with the pipe. This method of repair keeps the strain and stress in the damaged area of the pipe within acceptable limits, when full operational fluid pressures are applied within the pipe. If one layer of substrate cannot withstand the tension created by the shared hoop stress, additional layers of substrate are overlapped for added strength. As more layers of substrate are wrapped, there is a corresponding larger amount of hoop stress absorbed by the substrate and taken away from the pipe.
Further, the amount of substrate overlapping on the previously wrapped substrate corresponds directly to the amount of strength added to the pipe by the repair. For a smaller operational pipe pressure, a smaller amount of overlap is preferred. If there is too much overlap for the design pressures, the repair is too costly. For a higher design hoop stress, a larger substrate overlap is preferred. If there is not enough overlap, the substrate repair does not have enough strength to withstand the design pressures and the pipe will strain and become further damaged.
The layered structure results in a partial overlap between adjacent layers. The partial overlap of the adjacent layers renders the substrate being angled relative to the central axis of the. structure, or having a spiral-shape or helix-shape wrapping material about the structure. With a low helix pitch, there is a greater the amount of overlapping substrate. Conversely, with a greater helix pitch, there is a lesser amount of substrate that overlaps.
The most common structures that are repaired by way of wrapping with a flexible substrate are cylindrical structures, such as utility poles, architectural and industrial support columns, and pipes. However, other shaped structures, with both regular and irregular cross-section can also often be advantageously repaired by way of wrapping the structure with a flexible reinforcing substrate.
In order for the amount of overlapping of a flexible repair substrate to be at a consistent, economical, and structurally adequate level, the helix pitch of the substrate is controlled during application. The method of controlling the helix pitch involves aligning an edge of an overlapping flexible reinforcing substrate with visible indicia along the length of the previously wrapped substrate. Providing a guide to allow easy, accurate application of a reinforcing wrap is particularly helpful to minimize errors when the wrap is not easily removable once applied, because of strong adherence of successive wraps of the substrate to each other, for example.
When using the flexible reinforcing substrate with indicia along the substrate for controlling helix pitch or overlap as provided herein, the user begins by affixing, either permanently or removably, a transverse edge of the substrate to the damaged article. Then, the user wraps the substrate around the damaged article. As the substrate begins to overlap, the user aligns the edge of the substrate of the overlapping layer with the desired indicium provided for the desired helix pitch. Thereafter, the user merely maintains the alignment of the edge of the substrate with that indicium as the substrate is wrapped around the damaged article. When the desired coverage of the damaged article has been achieved, the user simply cuts off any excess substrate and affixes the trailing end of the substrate to the damaged article, either permanently or removably, as desired in a particular application.
When there is a constant amount of overlapping substrate, there is a constant amount of tensile strength provided by the substrate along the length of the completed repair. The amount of tensile strength (or overlapping substrate) that is needed to adequately repair the pipe is determined by the operational design pipe pressure. Each indicator on the substrate corresponds to a different level of tensile strength. As long as the design pipe pressure is known, the user knows which of several visible indicia to follow.